Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 211654

Area Forecast Discussion
National Weather Service Seattle WA
855 AM PST Mon Jan 21 2019

.SYNOPSIS...Weak high pressure will produce a break in
precipitation today into tonight. A pair of frontal systems will
give rain at times Tuesday into Wednesday. A ridge of high pressure
aloft will bring about another period of dry weather Thursday into
early next week.


.SHORT TERM...Plenty of low clouds over much of W WA this morning
with temperatures starting off a little brisk with many locations
reporting temps in the lower to mid 30s...although SeaTac is proving
to be the local hot spot currently observing 40 degrees. Some
isolated showers are present on the radar...but are generally light
and look to be pretty short lived.

A weakening upper level ridge will keep conditions quiet over W WA
again today. Low clouds and fog were slow to burn off
yesterday...but with some breaks in the cloud cover already starting
to occur...thanks to a look out the hopeful that lower
clouds will give way to mid level or high clouds in advance of
upcoming system for Tuesday.

Speaking of which...looking at next system making its way to the
coast early Tuesday morning bringing the usual mix of wind and rain
to the area. Winds will be breezy to locally windy for the
area...however speeds do not look to encroach on headline worthy
thresholds at this time. This initial system has a hard time staying
together as it moves eastward and as such precip amounts look to be
initially light. A secondary system looks a bit wetter though as it
follows right on the heels of the first one...impacting the area
Tuesday afternoon and evening. This will allow for the breezy/windy
conditions to persist into Wednesday...but will also result in
rising snow levels. THis system does not look to linger very
long...being east of the Cascades just after sunset Wednesday.
Models remain on track for upper level ridging to start building into
the area overnight Wednesday and into Thursday.

Inherited forecast looks good with no need for any morning updates.


.LONG TERM...From Previous Discussion...Models remain in good
agreement with an upper ridge building into the region Thursday
through Saturday for another dry period along with near or slightly
above normal daytime temperatures. By late in the weekend, both the
GFS and the Euro retrograde the ridge axis offshore. The Euro is
more aggressive with this idea and allows a weak system to clip the
area from the northwest on Sunday. This is a relatively new idea in
the models and, as such, no significant changes were made to the
extended forecast overnight.   27


.AVIATION...An upper ridge over the area today will weaken tonight
as a frontal system moves into the area. At the surface, weak high
pressure over the area today will shift inland tonight with
increasing southeasterly gradients as the frontal system nears. The
air mass is stable.

Ceilings mostly 4000-6000 feet this morning but with pockets of MVFR
ceilings and isolated IFR ceilings and fog, mainly over the south
interior. The general trend should be for improving conditions today
as the low levels dry a bit. Low and mid clouds will increase again
tonight and Tuesday morning as rain develops.

KSEA...Ceilings 4000-5000 feet this morning. Ceilings could lower at
times this morning but the general trend should be for improving
conditions by afternoon. Ceilings will lower again tonight and
Tuesday morning as a front moves onshore and rain develops.
Southerly wind 3-6 knots. Schneider


.MARINE...Winds will be fairly light today with high pressure over
the area. A frontal system will move into the area tonight and
Tuesday and then inland Tuesday night and Wednesday. Southerly small
craft advisory winds are likely most waters during this period.
Marginal gales are possible at times Coastal Waters, entrances to
the Strait, and Northern Inland Waters. Will look at this closer
after the 12Z guidance comes in this morning.

Winds will be relatively light again Thursday and Friday with weak
high pressure over the area.

Minor tidal overflow is possible at the coast early this afternoon
and again early Tuesday afternoon due to high astronomical tides and
slight pressure anomalies. The better chance looks like it will be
on Tuesday when atmospheric pressures are a little lower and
resultant anomalies are a bit larger. A similar round of minor tidal
overflow is possible for the inland Waters late Wednesday morning.



.HYDROLOGY...From Previous Discussion...The idea that a couple of
weak fronts would just brush the area Tuesday and Wednesday is
trending toward wetter solutions. Considering how easily the
Skokomish river made it up to flood stage with this past front, I
think now that the river forecast bears watching for the middle of
the week. For now, I just have the river starting upward again on
Tuesday and do not have a forecast for Wednesday--but that`s the day
to watch of the models keep up this trend. Elsewhere, river flooding
is not expected over the next 7 days.


WA...Coastal Flood Advisory until 3 PM PST this afternoon for Central

     Coastal Flood Advisory from noon to 4 PM PST Tuesday for Central

PZ...Small Craft Advisory from 8 PM this evening to 10 AM PST
     Wednesday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From Cape Flattery To
     James Island Out 10 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From James
     Island To Point Grenville Out 10 Nm-Coastal Waters From
     Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory from midnight tonight to 7 AM PST Wednesday
     for Admiralty Inlet-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands-Puget Sound and Hood Canal-West Entrance U.S.
     Waters Strait Of Juan De Fuca.


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